The present invention relates to an icebreaker with the maximum icebreaking waterline width in its forebody and with trimming and ballasting means.
It is known that icebreacking ships can more effectively break ice the further forward is displaced the widest part of the icebreaking waterline in the headway direction. This improvement is reversed in the case of sternway movement.
For certain icebreakers with special tasks, such as e.g. convoy icebreakers, significance is not only attached to the capacity of effectively being able to break ice when making headway, but also the capacity to rapidly change the direction of travel and also to be able to break a fixed ice cover in the case of sternway travel.
EP-A-No. 0070002 discloses a ship for travelling in open or ice-covered water with a pontoon-like forebody located above the waterline, which has parallel side walls and an end face extending over the entire breadth of the ship and which under water is planar and markedly forwardly inclined, which towards the stern passes into a centre keel, whilst also having an afterbody having drive means housed therein, in which the lateral edges in the transition region of the forebody side walls to the end face are curved in the longitudinal direction of the lateral edges and project in such a way sideways with respect to the planes formed by the forebody side walls, that the distance between the lateral edges located under the construction line forms the maximum underwater hull width. The undersides of the frames between the two lateral edges from the point of the ship's length at which the end face passes into the centre kneel, to the point at which it reaches the ship's bottom are constructed athwartships downwardly curved or bent. In the case of a ship constructed in this way more favourable conditions are provided for shear fracture of a one-part floe from the fixed ice cover and the guidance of the floe beneath the water is improved, with a reduce risk of crushing the floe into small fragments, so that it is possible to even more reliably ensure that the floe is brought under the fixed ice cover.
If in the case of an icebreaker constructed in this way headway travel takes place on the normal icebreaking waterline and sternway travel on the trimmed waterline, the following situation arises. In the case of headway, two lateral cutting edges provided on the prow produce a smoothly cut, ice-free fracture channel in the ice cover and regularly shaped, approximately rectangular ice floes are moved laterally beneath the unbroken ice cover and are removed from the region of the propeller. In the case of sternway travel, e.g. through the laterally projecting cutting edges located on the bow and forming the widest part of the hull, a fracture channel is produced in the ice, in that the broken ice is raised to the sides in the same way as by a snow plough. In this case, it is neither possible to prevent ice contact with the propeller, nor the entry of broken ice into the channel.